1. Field of the Invention
The present invention relates to an image display apparatus, such as a liquid crystal projector, and more specifically pertains to a technique of compensating for a variation in chromaticity coordinate of a color ray emitted from a display device with a variation in tone of an input color signal.
2. Description of the Related Art
A three panel-type liquid crystal projector, one of image display apparatuses, has three liquid crystal panels respectively corresponding to three colors R (red), G (green), and B (blue) as display devices. In this liquid crystal projector, illumination light emitted from a lighting optical system is divided into respective color rays R, G, and B, which enter the liquid crystal panels of the corresponding colors. In response to input of each of R, G, and B signals as image signals into the liquid crystal panel of the corresponding color, the liquid crystal panel is actuated to transmit the incident color ray. The R, G, and B transmitted rays (color rays) emitted from the three liquid crystal panels are mixed and are projected on a screen by means of a projection optical system. A resulting color image according to the R, G, and B signals is thus displayed on the screen.
The liquid crystal panel used for the liquid crystal projector varies the wavelength characteristic of the transmitted ray with a variation in tone of the input signal.
For example, the wavelength characteristic of the R color ray transmitted through the R liquid crystal panel is varied with a variation in tone value of the input R signal. The color of the R transmitted ray may thus approach to magenta or to orange. Namely the variation in tone of the R signal results in varying the chromaticity coordinate of the R transmitted ray, which is supposed to be fixed regardless of the varying tone of the R signal.
The similar phenomena are observed in the G liquid crystal panel and the B liquid crystal panel with a variation in tones of the input G signal and B signal.
The liquid crystal projector mixes the R, G, and B transmitted rays by the additive color mixing technique according to the input R, G, and B signals to reproduce the color of an image, on the assumption that the chromaticity coordinates of the R, G, and B transmitted rays (color rays) emitted from the respective liquid crystal panels are not varied with a variation in tones of the R, G, and B signals. The varying chromaticity coordinates of the R, G, and B transmitted rays with a variation in tones of the R, G, and B signals, however, prevent accurate color reproduction of the image according to the input R, G, and B signals.